The present invention relates to methods and apparatus for centering an elongate object passing through an opening. More particularly, the present invention relates to an apparatus for centering a pipe passing through a circular opening. Still more particularly, the present invention relates to centering a tubular in a set of slips on a drilling rig.
In rotary drilling applications, a tubular drill string is formed from a series of connected lengths of drill pipe. The individual lengths of drill pipe are joined by threaded connections. During the drilling and completion of a well, the drill string must occasionally be pulled from the well and reinstalled. The process of pulling or installing the drill string is referred to as “tripping.” Other tubular strings used in well construction, such as casing and tubing strings, may also be tripped into and out of a well during drilling operations.
During tripping, the threaded connections between the lengths of drill pipe are connected and disconnected as needed. When the uppermost pipe is disconnected, the weight of the drill string is supported by slips positioned in the drill floor. Slips generally operate by inserting a wedge-shaped gripping member into the annular area between the tubular member and a fixed slip bowl. Some automatic slip assemblies operate by hydraulically engaging the tubular with a gripping member. Regardless of the configuration of the slips, almost all slip assemblies rely on the tubular being relatively centered within the assembly so that the gripping members uniformly engage the tubular.
However, due to the nature and structure of drilling rigs, the pipe string is sometimes not centered in the slips. A situation where the pipe is not centered when the slips are set can damage the pipe string and other equipment and possibly dropping of the pipe string, which can lead to delays and increased costs. Thus, it is very important to be able to center the pipe string to facilitate proper installation of the slips.
Therefore, the embodiments of the present invention are directed to methods and apparatus for centering a pipe string that seek to overcome certain of these and other limitations of the prior art.